[BUG] Valid text incorrectly parsed as empty, causing unrecoverable 400 error

Preflight Checklist

• [x] I have searched existing issues and this hasn't been reported yet
• [x] This is a single bug report (please file separate reports for different bugs)
• [x] I am using the latest version of Claude Code

What's Wrong?

Bug: Valid text content blocks incorrectly interpreted as empty, causing unrecoverable 400 errors

Description

Claude Code incorrectly interprets valid, non-empty text content blocks as empty/whitespace-only, triggering API 400 errors. Once this occurs, all subsequent API calls fail, including /compact, making it impossible to continue the session without losing all context.

Error Message

API Error: 400 {"type":"error","error":{"type":"invalid_request_error","message":"messages: text content blocks must contain non-whitespace text"},"request_id":"req_011CXorGXRzZRLY5fcRKndS7"}

Expected Behavior

• Valid text content should be correctly transmitted to the API
• Messages with actual content should never trigger "must contain non-whitespace text" errors

Actual Behavior

• Non-empty text content is being misinterpreted as empty
• The API rejects the request with a 400 error
• No recovery path exists other than /clear, which destroys all context
• /compact fails with the same error, offering no escape

Impact

• High friction: Users lose significant context and must rebuild expensive conversation state
• No warning: The error occurs suddenly with no indication of root cause
• No recovery: Even built-in recovery tools (/compact) fail
• Silent corruption: Users have no visibility into what went wrong with their valid input

Environment

• Claude Code Version: [2.1.31]
• OS: [macOS 15.7.3,]
• Shell: [zsh]
• Terminal: [Terminal.app]
• Locale/Encoding: [US.UTF-8]

Additional Context

• The user's input is valid and non-empty
• There is no indication of what content is being misinterpreted
• Long coding sessions accumulate significant context that is expensive to rebuild
• Users have no way to inspect the conversation history to diagnose the issue

What Should Happen?

Error 400, 500, or other similar issues should not require context destruction.

Error Messages/Logs

Steps to Reproduce

1. Use Claude Code (CLI) in a session with accumulated context
2. At some point (trigger unclear), a valid message is incorrectly parsed/encoded
3. Attempt to continue the conversation → 400 error
4. Attempt /compact to recover → Same 400 error
5. Session is now unrecoverable; context must be rebuilt

Claude Model

Sonnet (default)

Is this a regression?

Yes, this worked in a previous version

Last Working Version

_No response_

Claude Code Version

2.1.31

Platform

Anthropic API

Operating System

macOS

Terminal/Shell

Terminal.app (macOS)

Additional Information

_No response_